1. Field of the Invention
The present invention relates to an optical disk device, and particularly relates to an optical disk device including a mechanism that moves light beams to a working position.
2. Description of the Background Art
As to an optical disk device, Japanese Patent Laying-Open No. 2005-071395 discloses an optical disk device provided with a shaft sliding-type optical pick-up. The optical pick-up has a semiconductor laser, an objective lens, a light-detecting element, a lens holder holding the objective lens, a guide shaft fitted into a bearing portion provided at the lens holder and capable of sliding the lens holder in a direction parallel to an optical axis of the objective lens, a focusing servomechanism including a focusing coil, a yoke, and a permanent magnet, and a tracking servomechanism including a tracking coil, a yoke, and a permanent magnet. The semiconductor laser outputs laser beams to the optical disk. The objective lens focuses the laser beams output from the semiconductor laser onto a data-recording surface of the optical disk. The light-detecting element receives light reflected from the optical disk and converts the light into an electrical signal. The guide shaft journals the lens holder rotatably in a direction orthogonal to the optical axis. The focusing servomechanism moves the lens holder in a direction parallel to the optical axis. The tracking coil rotates the lens holder in the direction orthogonal to the optical axis. For a focus-on operation, the optical pick-up drives the focusing coil to perform the focus-on operation, while repetitively causing a slight displacement of the bearing portion of the lens holder with respect to the guide shaft in the direction orthogonal to the optical axis by applying to the tracking coil a prescribed voltage and a wobble signal of a triangular waveform having a prescribed frequency. The focus-on operation is thereby stabilized.
According to the invention disclosed in Japanese Patent Laying-Open No. 2005-071395, the focus-on operation can be stabilized.
Japanese Patent Laying-Open No. 2005-332554 discloses a reproduction device reproducing a recording medium having a plurality of recording layers. The reproduction device is provided with optical head means, shaft sliding-type focus actuator means, focus servo means, and focus jump control means. The optical head means applies laser light to each of the recording layers by using an objective lens as an output terminal, detects information on light reflected from each of the recording layers, and reads information recorded on each of the recording layers. The focus actuator means holds the objective lens movably in a direction toward and from the recording medium. The focus servo means generates a focus servo driving signal based on a focus error signal obtained from the reflected light information read by the optical head means, and drives the focus actuator means such that the laser light is kept in a focused state with respect to a recording layer to be reproduced. The focus jump control means generates a kick signal initiating a focus jump movement caused by the focus actuator means, and a brake signal terminating the focus jump movement, as focus jump driving signals for bringing a transition from a focused state with respect to a recording layer to a focused state with respect to another recording layer. The focus jump control means generates the kick signal as a signal having its kick driving force increased from an initial value.
According to the invention disclosed in Japanese Patent Laying-Open No. 2005-332554, a stable focus jump operation can be maintained.
However, the invention disclosed in Japanese Patent Laying-Open No. 2005-071395 has a problem of difficulty in stabilizing the focus jump operation (hereinafter referred to as “focus jump”). The “focus jump” refers to a transition from a state where recording or reading can be performed on a recording layer, to a state where recording or reading can be performed on another recording layer, when information is recorded on or read from an optical disk having a plurality of recording layers.
In the invention disclosed in Japanese Patent Laying-Open No. 2005-071395, a control portion performs a process of applying a wobble signal to the tracking coil in the focus-on operation. In this case, no control is required for the tracking coil until just before the focus-on operation. This makes it easy for the control portion to control the tracking coil in a prompt manner.
In contrast, in the case of the focus jump operation, control over the tracking coil may be required until just before the focus jump operation. This is because the optical pick-up operates until just before the focus jump. When the optical pick-up operates until just before the focus jump, it is difficult to abruptly modify the control over the tracking coil. This is because the time required for a process for modifying the control over the tracking coil is extremely short, while the time permitted for modifying the control over the tracking coil is much shorter. The time required for the focus jump is merely a few microseconds.
The invention disclosed in Japanese Patent Laying-Open No. 2005-332554 has a problem of prolonged time required for the focus jump.